1. Field of the Invention
The present invention relates to a non-aqueous pigment ink.
2. Description of the Related Art
An inkjet recording system is a printing system in which printing is conducted by spraying a liquid ink with a high degree of fluidity from very fine nozzles, and adhering that ink to a recording medium such as a sheet of paper. These systems enable the printing of high-resolution, high-quality images at high speed and with minimal noise, using a comparatively inexpensive printing apparatus, and are rapidly becoming widespread.
The coloring materials for the inks used in these inkjet recording systems can be broadly classified into materials that use pigments and materials that use dyes. Of these, there is a growing tendency for the use of inks that use pigments as the coloring materials, as such inks exhibit the excellent levels of light resistance, weather resistance and water resistance that are required for high image quality printing.
In terms of the solvent, inks can be broadly classified into aqueous inks and non-aqueous inks. Non-aqueous inks that do not use water as the ink solvent, including solvent-based inks that use a volatile solvent as the main constituent and oil-based inks that use a non-volatile solvent as the main constituent, exhibit superior stability within the printer (such as intermittent dischargeability and discharge recovery following standing idle for a long period), cause no curling of the printed paper and have a short ink penetration and drying time, and are therefore attracting considerable attention.
The nozzle plate surface of the inkjet head is subjected to an ink repellent treatment using a fluorine-based process or the like. The cleaning of this type of nozzle plate surface is performed by discharging a small amount of ink, suctioning the ink off with a suction device, and wiping the plate surface with a wiper blade. Abrasion of the nozzle blade surface by the wiper blade can cause a deterioration in the ink repellency of the nozzle plate surface.
If the ink repellency of the nozzle plate surface deteriorates, then the wettability of the plate surface by non-aqueous inks increases, which causes ink to adhere to the nozzle plate surface, and can cause discharge defects. Accordingly, it is important that a non-aqueous ink is provided that improves the ink repellency at the nozzle plate surface.
Increasing the polarity of the ink solvent and lowering the viscosity of the ink are effective in improving the ink repellency of the ink at the nozzle plate surface. However, polar solvents that have a low viscosity generally have a high degree of volatility, which means the stability of the ink within an inkjet printer may not be able to be favorably maintained.
Patent Document 1 (Japanese Patent Laid-Open No. 2007-126564) discloses an ink comprising an ester solvent, an alcohol solvent and a hydrocarbon solvent as the ink solvents, wherein the toner solubility properties are improved by specifying the polarity of the ester solvent. Although this ink exhibits excellent stability within the printer and excellent toner solubility properties, when the nozzle plate surface of the inkjet head deteriorates as a result of usage over a long period, the ink repellency deteriorates, meaning the ink discharge performance and the image quality may deteriorate.